Electronic devices in which operations are carried out by touching images such as icons displayed on a screen are commonly used. Display panels used in electronic devices such as this are called touch panels (or touch screens). In touch panels, capacitance touch sensors are used. In capacitance touch sensors, changes in electrical capacity are detected as input signals between a pair of sensor electrodes called Tx electrodes and Rx electrodes.
Conventional touch panels have a structure in which a touch sensor panel and a display panel overlap. However, In the structure in which the two panels are superimposed, there is a problem that the thickness of the display device increases. For example, in display devices that are bent and folded, called flexible displays, a structure in which a sensor panel and a display panel overlap impedes flexibility.
A structure with touch sensor functions built into a display panel is disclosed. For example, as a display panel using organic electroluminescence elements (hereinafter referred to as organic EL elements), a display device called an in-cell type provided with a touch sensor inside the panel, arranged with a first detection electrode and a second detection electrode to sandwich an inorganic insulating film provided as a sealing layer is disclosed (see Japanese Laid-Open Patent Publication No. 2015-050245.)
A sealing film provided in a display device without defects is desired. If defects exist in the sealing film, moisture and the like enter the region where display elements and circuit elements are formed, causing properties of the elements to deteriorate. For example, since the organic EL elements provided in the pixels deteriorate due to moisture and the like, defects in the sealing film cause display defects.
A dense sealing film blocking the entrance of moisture is formed in a thin film process by Plasma CVD (Chemical Vapor Deposition) method and the like. One cause of defects in the sealing film is foreign matter attached to the surface on which the film is being formed. For example, before manufacturing the sealing film, when foreign matter such as particles are attached to the surface of the substrate on which the film is formed, the sealing film is not evenly formed and defects are generated in the regions in which foreign matter is attached. As a result, moisture enters from the defective parts of the sealing film, and deterioration of the organic EL elements progresses.
A process for forming a first detection electrode before forming the sealing film is included in the display device disclosed in Japanese Laid-Open Patent Publication No. 2015-050245. It is common to form a conducting film for forming the first detection electrode by a sputtering method and the like. The film formation process by a sputtering method is one cause of the generation of foreign matter. In this process, when the sealing film is formed with foreign matter attached, defects are generated in the sealing film. Furthermore, when the second detection electrode is formed sandwiching a sealing film including defective parts, the first detection electrode and the second detection electrode short circuit.